Reducing tire rolling resistance through pre-heating

ABSTRACT

A system for and method of reducing the rolling resistance of a tire by pre-heating the tire prior to use.

RELATED APPLICATIONS

This patent application claims priority to, and benefit from U.S. Provisional Patent Application Ser. No. 61/075,018, entitled “METHODS OF ENHANCING TIRE PERFORMANCE UTILIZING ACTIVE MATERIALS,” and filed on Jun. 24, 2008, the disclosure of which being incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure generally relates to tires, such as automobile tires, and to methods of improving tire performance. More particularly, the invention concerns a system for and method of reducing rolling resistance through pre-heating and to tires adapted to perform the same.

2. Discussion of Prior Art

Properly functioning tires are important in maintaining optimal fuel efficiency. Perhaps the most important performance characteristic to that end is “rolling resistance,” which is the tendency for a tire to stop rolling under load due in large to the hysteretic losses in the tire material. Many variables and conditions play a role in determining the rolling resistance of a tire, including ambient and inherent conditions such as the outside temperature and moisture content, the air pressure inside the tire, and the stiffness and temperature of the tire material. More particularly, with respect to the latter, it is appreciated that rolling resistance decreases as the tire warms up due to two principal causes, the temperature related increase in tire inflation pressure with an accompanying decrease in tire deformation, and the fact that hysteresis in the “rubbery” tire material is a decreasing function of temperature. Concernedly, despite the desire to maintain optimal rolling resistance across differing conditions, conventional tires typically present non-adaptive solutions.

BRIEF SUMMARY

The present invention concerns a system for and method of reducing the rolling resistance of a tire through pre-heating. As such, the invention is useful for enabling optimal tire performance over a wider range of ambient start-up temperatures. The invention is further useful for tuning characteristics of the tire, and thus improving fuel economy. The inventive tire, in some embodiments, uses active material enabled means to reliably and rapidly achieve and then maintain desired temperatures.

In general, the method is performed by and the system includes a tire employable by a vehicle traveling upon a surface, so as to define an associative rolling resistance value. However, it is certainly appreciated that the system may be employed when the vehicle is parked on the surface. The system is adapted to selectively modify the resistance value through pre-heating of at least a portion of the tire. In a preferred embodiment, the tire includes a structural component, and at least one heating element inter-engaged with and operable to selectively raise the temperature of at least a portion of the component, when activated, actuated or otherwise heated. An external device or power source may be used to heat the element.

The above described and other features are exemplified by the following figures and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described in detail below with reference to the attached drawing figures of exemplary scale, wherein:

FIG. 1 is an elevation of a vehicle upon a surface, including a sensor, and adaptive tire being pre-heated by an external device, in accordance with a preferred embodiment of the invention;

FIG. 2 is a perspective view of adaptive tire having circumferential heating elements, in accordance with a preferred embodiment of the invention;

FIG. 3 is a cross-sectional view of the tire shown in FIG. 2, particularly illustrating the heating elements, and structural components, including bead wires, tread elements, reinforcing belts, a wheel, and a thermoelectric element attached to the wheel, in accordance with a preferred embodiment of the invention; and

FIG. 4 is a perspective view of adaptive tire being heated by an external power source through inductance, in accordance with a preferred embodiment of the invention.

DETAILED DESCRIPTION

The present invention generally concerns a system 10 for and method of reducing the rolling resistance of a tire 12 through pre-heating. That is to say, in the present invention, the tire 12 is heated prior to use, and is particularly suited to prevent traditional cold state rolling resistance concerns. As such, a solution is presented that is responsive to the afore-mentioned concerns regarding the effect of rolling resistance on fuel (e.g., electric charge) economy. The invention is described and illustrated herein with respect to an automotive vehicle 14 (e.g., motorcycle, car, truck, SUV, all-terrain vehicle, etc.) that travels upon a surface 16; however, it is certainly appreciated that the advantages and benefits thereof could be used in other applications, such as bicycles and the like.

As best shown in FIGS. 2 and 3, the inventive implements of the system 10 are adapted for use with an otherwise conventional elastomeric (e.g., synthetic and/or natural rubber) tire that exhibits a rolling resistance value when caused to roll upon a surface under load. The tire may be of the type defining an interior region when mounted upon a wheel 18, and including an air valve assembly 20, first and second opposite sidewalls 22 interconnected by a treadwall 24. Underneath the treadwall 24, a layer of reinforcing belts or piles 26 typically formed of steel, add structural stability and adds puncture resistance to the treadwall 24. It is appreciated that the afore-described structural components are described for exemplary purposes only, the present invention may be used with various tire configurations and structural components not mentioned herein.

The sidewalls 22 provide lateral stability to the tire 12 and contribute to the rolling resistance value. More particularly, it is appreciated that the tire 10 undergoes deformation (FIG. 1) as it rolls that is inversely proportional to the stiffness of the sidewalls 22. Moreover, the treadwall 24 also undergoes deformation, as it flattens into a contact patch defined by the tire 12 and surface 16. The resistance to flattening exhibited by the treadwall 24 also contributes to the overall rolling resistance. As such, the preferred system 10 is operable to at least pre-heat the sidewalls 22 and/or treadwall 24 of the tire 12, and more particularly, the radial outer half of the sidewalls 22 and the full width of the treadwall 24.

In a first embodiment, the tire 12 includes a pre-heating element 28 designed to selectively heat the surrounding components when excited, actuated, or activated (FIGS. 2-3). The element 28 is communicatively coupled to an external (e.g., off-board) power source or device 30 that provides the influx of energy, and primarily functions to convert the energy into heat. However, it is appreciated that the device 30 may be configured to deliver heat energy directly. In one example, wherein the tire 12 and wheel 18 cooperatively define a confined space, the element 28 may be a thermoelectric heater element 28 a disposed within and operable to heat the space. By heating the space, the element 28 a also heats the sidewalls 22 and treadwall 24. Alternatively it is appreciated that the thermoelectric element 28 a may be attached to the wheel 18 adjacent the space (FIG. 3).

In another example, the element 28 is formed of an active material (e.g., a shape memory alloy, electroactive polymer, and/or piezopolymer, in either the unimorphic or bimorphic forms). The active material element 28 preferably composes or is directly engaged with the targeted structural components of the tire 12. Here, the material is preferably thermally activated (e.g., the case with shape memory alloys), such that activation itself contributes heat energy to the surrounding component material and/or space. Where the active material is Martensitic shape memory alloy, it is appreciated that heating also results from the flexing (which is the case with activation of electroactive polymers, and/or piezopolymers, in either the unimorphic or bimorphic forms or the thermal activation of the shape memory effect in SMA) of the lossy tire material as well as the enthalpy of phase transformation, which occur over a complete actuation cycle. The preferred SMA element 28 is pre-stretched so that actuation more readily effects material flexure and displacement.

In another example, the element 28 is resistively heated to produce the desired temperature rise in the structural components of the tire 12. For example, the element 28 in this configuration may consist of a steel cord, carbon nanotube, or where Joule heated, a shape memory alloy wire preferably oriented circumferentially within the sidewall (FIG. 2) or treadwall 24 (FIG. 3). A plurality of elements 28 b are preferably offset, wherein the offset is based in part upon the individual resistance or heat generating capability of the elements 28 b.

The elements 28 are communicatively coupled to (e.g., via electric leads, wirelessly, etc.) an electrical power source 30. Where the elements 28 are electrically conductive, resistive heating may also be caused by inductance (FIG. 4). Here, the element 28 is communicatively coupled to an external field (or flux) of an external circuit, as typically presented by a transformer.

A preferred method of reducing the rolling resistance of a tire 12 includes determining or anticipating a cold state condition, wherein the temperature of the tire material will likely contribute to excessive rolling resistance. For example, it is appreciated that, except where ambient temperatures are sufficiently high, start-up operation (i.e., the first 20 to 30 minutes of operating a vehicle, which envelops most vehicle trips) often presents a cold state tire condition, and that such state may be longer, when ambient temperature is low. Moreover, the presence and evaporation of water will also slow tire warm up.

In a cold state condition, the tire 12 and/or power source 30 are maneuvered to a secure position relative to each other, such that the source 30 becomes thermally coupled to the element 28. The source 30 is then actuated to engage the element 28 and heat at least a portion of the tire 12. The system 10 is preferably configured to then determine or anticipate a warm state condition, and terminate actuation of the source 30 when the warm state condition is determined. For example, the system 10 may be configured to shut off after a predetermined period. As such, the preferred system 10 further includes at least one temperature sensor 32 and controller 34 communicatively coupled to the sensor 32.

The system 10 may be implemented in a garage setting wherein the vehicle 12 is parked. The external power source 30 may be a recharging station that is plugged into the vehicle 12 at a specified position within the garage. As a secondary function of the recharging system 30, the tire 12 may be pre-heated prior to vehicle operation by feeding a maintenance (or “trickle”) charge through resistive elements 28, or by cyclically actuating active material elements 28, so as to cause at least a portion of the tire 12 to repetitively flex over a hysteresis cycle.

As used herein the term “active material” shall be afforded its ordinary meaning as understood by those of ordinary skill in the art, and includes any material or composite that exhibits a reversible change in a fundamental (e.g., chemical or intrinsic physical) property, when exposed to an external signal source. Thus, active materials shall include those compositions that can exhibit a change in stiffness, modulus, shape and/or dimensions in response to the activation signal.

Depending on the particular active material, the activation signal can take the form of, without limitation, an electric current, an electric field (voltage), a temperature change, a magnetic field, a mechanical loading or stressing, and the like. For example, a magnetic field may be applied for changing the property of the active material fabricated from magnetostrictive materials. A heat signal may be applied for changing the property of thermally activated active materials such as SMA. An electrical signal may be applied for changing the property of the active material fabricated from electroactive materials, piezoelectrics, and/or ionic polymer metal composite materials.

Suitable active materials for use with the present invention include, without limitation, shape memory alloys (SMA), electroactive polymers (EAP), piezoelectric materials (both unimorphic and bimorphic), and the like. The active material element may take many geometric forms including pellets, beads, fillers, sheets, layers, and wires, wherein the term “wire” is further understood to encompass a range of longitudinal forms such as strands, braids, strips, bands, cables, slabs, springs, etc. To aid in embedding, the wires preferably present a non-circular cross-section, such as “T”-shape or polygonal cross-section.

More particularly, SMA generally refers to a group of metallic materials that demonstrate the ability to return to some previously defined shape or size when subjected to an appropriate thermal stimulus. Shape memory alloys are capable of undergoing phase transitions in which their yield strength, stiffness, dimension and/or shape are altered as a function of temperature. The term “yield strength” refers to the stress at which a material exhibits a specified deviation from proportionality of stress and strain. Generally, in the low temperature, or martensite phase, shape memory alloys can be plastically deformed and upon exposure to some higher temperature will transform to an austenite phase, or parent phase, returning to their shape prior to the deformation.

Shape memory alloys exist in several different temperature-dependent phases. The most commonly utilized of these phases are the so-called Martensite and Austenite phases discussed above. In the following discussion, the martensite phase generally refers to the more deformable, lower temperature phase whereas the austenite phase generally refers to the more rigid, higher temperature phase. When the shape memory alloy is in the martensite phase and is heated, it begins to change into the austenite phase. The temperature at which this phenomenon starts is often referred to as austenite start temperature (A_(s)). The temperature at which this phenomenon is complete is called the austenite finish temperature (A_(f)).

When the shape memory alloy is in the austenite phase and is cooled, it begins to change into the martensite phase, and the temperature at which this phenomenon starts is referred to as the martensite start temperature (M_(s)). The temperature at which austenite finishes transforming to martensite is called the martensite finish temperature (M_(f)). Generally, the shape memory alloys are softer and more easily deformable in their martensitic phase and are harder, stiffer, and/or more rigid in the austenitic phase. In view of the foregoing, a suitable activation signal for use with shape memory alloys is a thermal activation signal having a magnitude to cause transformations between the martensite and austenite phases.

Shape memory alloys can exhibit a one-way shape memory effect, an intrinsic two-way effect, or an extrinsic two-way shape memory effect depending on the alloy composition and processing history. Annealed shape memory alloys typically only exhibit the one-way shape memory effect. Sufficient heating subsequent to low-temperature deformation of the shape memory material will induce the martensite to austenite type transition, and the material will recover the original, annealed shape. Hence, one-way shape memory effects are only observed upon heating. Active materials comprising shape memory alloy compositions that exhibit one-way memory effects do not automatically reform, and will likely require an external mechanical force to reform-.

Intrinsic and extrinsic two-way shape memory materials are characterized by a shape transition both upon heating from the martensite phase to the austenite phase, as well as an additional shape transition upon cooling from the austenite phase back to the martensite phase. Active materials that exhibit an intrinsic shape memory effect are fabricated from a shape memory alloy composition that will cause the active materials to automatically reform themselves as a result of the above noted phase transformations. Intrinsic two-way shape memory behavior must be induced in the shape memory material through processing. Such procedures include extreme deformation of the material while in the martensite phase, heating-cooling under constraint or load, or surface modification such as laser annealing, polishing, or shot-peening. Once the material has been trained to exhibit the two-way shape memory effect, the shape change between the low and high temperature states is generally reversible and persists through a high number of thermal cycles. In contrast, active materials that exhibit the extrinsic two-way shape memory effects are composite or multi-component materials that combine a shape memory alloy composition that exhibits a one-way effect with another element that provides a restoring force to reform the original shape.

The temperature at which the shape memory alloy remembers its high temperature form when heated can be adjusted by slight changes in the composition of the alloy and through heat treatment. In nickel-titanium shape memory alloys, for instance, it can be changed from above about 100° C. to below about −100° C. The shape recovery process occurs over a range of just a few degrees and the start or finish of the transformation can be controlled to within a degree or two depending on the desired application and alloy composition. The mechanical properties of the shape memory alloy vary greatly over the temperature range spanning their transformation, typically providing the system with shape memory effects, superelastic effects, and high damping capacity.

Suitable shape memory alloy materials include, without limitation, nickel-titanium based alloys, indium-titanium based alloys, nickel-aluminum based alloys, nickel-gallium based alloys, copper based alloys (e.g., copper-zinc alloys, copper-aluminum alloys, copper-gold, and copper-tin alloys), gold-cadmium based alloys, silver-cadmium based alloys, indium-cadmium based alloys, manganese-copper based alloys, iron-platinum based alloys, iron-platinum based alloys, iron-palladium based alloys, and the like. The alloys can be binary, ternary, or any higher order so long as the alloy composition exhibits a shape memory effect, e.g., change in shape orientation, damping capacity, and the like.

Thus, for the purposes of this invention, it is appreciated that SMA's exhibit a modulus increase of 2.5 times and a dimensional change of up to 8% (depending on the amount of pre-strain) when heated above their Martensite to Austenite phase transition temperature. It is appreciated that thermally induced SMA phase changes are one-way so that a biasing force return mechanism (such as a spring) would be required to return the SMA to its starting configuration once the applied field is removed. Joule heating can be used to make the entire system electronically controllable. Stress induced phase changes in SMA are, however, two way by nature. Application of sufficient stress when an SMA is in its Austenitic phase will cause it to change to its lower modulus Martensitic phase in which it can exhibit up to 8% of “superelastic” deformation. Removal of the applied stress will cause the SMA to switch back to its Austenitic phase in so doing recovering its starting shape and higher modulus.

Piezoelectric materials can also comprise metals selected from the group consisting of lead, antimony, manganese, tantalum, zirconium, niobium, lanthanum, platinum, palladium, nickel, tungsten, aluminum, strontium, titanium, barium, calcium, chromium, silver, iron, silicon, copper, alloys comprising at least one of the foregoing metals, and oxides comprising at least one of the foregoing metals. Suitable metal oxides include SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2, TiO.sub.2, SrTiO.sub.3, PbTiO.sub.3, BaTiO.sub.3, FeO.sub.3, Fe.sub.3O.sub.4, ZnO, and mixtures thereof and Group VIA and IIB compounds, such as CdSe, CdS, GaAs, AgCaSe.sub.2, ZnSe, GaP, InP, ZnS, and mixtures thereof. Preferably, the piezoelectric material is selected from the group consisting of polyvinylidene fluoride, lead zirconate titanate, and barium titanate, and mixtures thereof.

Electroactive polymers include those polymeric materials that exhibit piezoelectric, pyroelectric, or electrostrictive properties in response to electrical or mechanical fields. An example of an electrostrictive-grafted elastomer with a piezoelectric is poly(vinylidene fluoride-trifluoro-ethylene) copolymer. This combination has the ability to produce a varied amount of ferroelectric-electrostrictive, molecular composite systems. These may be operated as a piezoelectric sensor or even an electrostrictive actuator.

Materials suitable for use as an electroactive polymer may include any substantially insulating polymer or rubber (or combination thereof) that deforms in response to an electrostatic force or whose deformation results in a change in electric field. Exemplary materials suitable for use as a pre-strained polymer include silicone elastomers, acrylic elastomers, polyurethanes, thermoplastic elastomers, copolymers comprising PVDF, pressure-sensitive adhesives, fluoroelastomers, polymers comprising silicone and acrylic moieties, and the like. Polymers comprising silicone and acrylic moieties may include copolymers comprising silicone and acrylic moieties, polymer blends comprising a silicone elastomer and an acrylic elastomer, for example.

Materials used as an electroactive polymer may be selected based on one or more material properties such as a high electrical breakdown strength, a low modulus of elasticity—(for large or small deformations), a high dielectric constant, and the like. In one embodiment, the polymer is selected such that is has an elastic modulus at most about 100 MPa. In another embodiment, the polymer is selected such that is has a maximum actuation pressure between about 0.05 MPa and about 10 MPa, and preferably between about 0.3 MPa and about 3 MPa. In another embodiment, the polymer is selected such that is has a dielectric constant between about 2 and about 20, and preferably between about 2.5 and about 12. The present disclosure is not intended to be limited to these ranges. Ideally, materials with a higher dielectric constant than the ranges given above would be desirable if the materials had both a high dielectric constant and a high dielectric strength. In many cases, electroactive polymers may be fabricated and implemented as thin films. Thicknesses suitable for these thin films may be below 50 micrometers.

As electroactive polymers may deflect at high strains, electrodes attached to the polymers should also deflect without compromising mechanical or electrical performance. Generally, electrodes suitable for use may be of any shape and material provided that they are able to supply a suitable voltage to, or receive a suitable voltage from, an electroactive polymer. The voltage may be either constant or varying over time. In one embodiment, the electrodes adhere to a surface of the polymer. Electrodes adhering to the polymer are preferably compliant and conform to the changing shape of the polymer. Correspondingly, the present disclosure may include compliant electrodes that conform to the shape of an electroactive polymer to which they are attached. The electrodes may be only applied to a portion of an electroactive polymer and define an active area according to their geometry. Various types of electrodes suitable for use with the present disclosure include structured electrodes comprising metal traces and charge distribution layers, textured electrodes comprising varying out of plane dimensions, conductive greases such as carbon greases or silver greases, colloidal suspensions, high aspect ratio conductive materials such as carbon fibrils and carbon nanotubes, and mixtures of ionically conductive materials.

Materials used for electrodes of the present disclosure may vary. Suitable materials used in an electrode may include graphite, carbon black, colloidal suspensions, thin metals including silver and gold, silver filled and carbon filled gels and polymers, and ionically or electronically conductive polymers. It is understood that certain electrode materials may work well with particular polymers and may not work as well for others. By way of example, carbon fibrils work well with acrylic elastomer polymers while not as well with silicone polymers.

As used herein, the terms “first”, “second”, and the like do not denote any order or importance, but rather are used to distinguish one element from another, and the terms “the”, “a”, and “an” do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. Furthermore, all ranges directed to the same quantity of a given component or measurement is inclusive of the endpoints and independently combinable.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 

1. A tire employable by a vehicle traveling upon a surface, so as to define an associative rolling resistance value, and adapted to selectively modify the value, said tire comprising: a structural component; and at least one heating element inter-engaged with and operable to selectively raise the temperature of at least a portion of the component, so as to modify the resistance to a second value.
 2. The tire as claimed in claim 1, wherein the component cooperatively defines a confined space, and the element is a thermoelectric heater element disposed within and operable to heat the space.
 3. The tire as claimed in claim 1, wherein the element comprises a thermally activated active material operable to selectively raise the temperature of at least a portion of the component, when the element is activated.
 4. The tire as claimed in claim 3, wherein the heating element comprises shape memory alloy, electroactive polymer, and/or piezopolymer, and is cyclically activated.
 5. The tire as claimed in claim 1, wherein the element is resistively heated, and selectively coupled to an electrical power source.
 6. The tire as claimed in claim 5, wherein the element is selected from the group consisting essentially of steel cords, carbon nanotubes, and shape memory alloys wires.
 7. The tire as claimed in claim 5, wherein resistive heating is caused by inductance, and the element is electrically conductive and communicatively coupled to an external field.
 8. A system for selectively reducing the rolling resistance of a tire, said system comprising: a tire including a structural component, wherein the component is deformed when the tire rolls and presents a first stiffness, and a pre-heating element thermally coupled to the component; and an external power source communicatively coupled to, and operable to heat the element, when caused to become inter-engaged therewith, said source and element being cooperatively configured to heat the component, and change the stiffness, so as to reduce the rolling resistance.
 9. The system as claimed in claim 8, further comprising: a sensor operable to determine a cold state condition of the tire; and a controller communicatively coupled to the sensor, and operable to cause the source to heat the element, when the condition is determined.
 10. A method of reducing the rolling resistance of a tire, said method comprising: a. determining a cold state condition of the tire; b. securing an external power source relative to the tire, wherein the source is operable to heat at least a portion of the tire; c. actuating the source so as to heat said at least portion; and d. determining a warm state condition and terminating actuation of the source.
 11. The method claimed in claim 10, wherein the tire includes at least one pre-heating element, and the source and element are communicatively coupled.
 12. The method claimed in claim 11, wherein the element is resistively heated, and the source is electrically coupled thereto.
 13. The method claimed in claim 12, wherein said element is resistively heated, the tire composes a vehicle, the source is a recharging station within a parking garage, and step c) further includes the step of electrically coupling the station to the tire, so as to cause a trickle charge to flow through said element, when the vehicle is parked within the garage.
 14. The method claimed in claim 12, wherein the element is a thermally activated active material element, and the source is operable to activate the element.
 15. The method claimed in claim 12, wherein the element is an active material element operable to cause at least a portion of the tire to flex when activated, and the source is configured to cyclically activate the element so as to cause said at least portion of the tire to repetitively flex over a hysteresis cycle.
 16. The method claimed in claim 15, wherein the element is a pre-stretched Martensitic shape memory alloy element. 